Three dimensional ultrasound imaging is one of the most significant challenges, and potentially rewarding efforts, in medical imaging. To retain the traditional benefit of ultrasound, visualization of dynamic biological processes such as heart motion, it is necessary to establish scanning as a purely electronic process. Two dimensional arrays are necessary for this achievement, though there are significant challenges to fabrication of these devices. A fine pitch must be achieved for quality imaging, though the resulting elements possess a very high electrical impedance and poor matching to electronics. Connection to these elements is difficult due to the large number and orientation, and dicing of such fine structures often results in missing elements. To overcome these issues, TRS proposes to make multilayer single crystal 2- D arrays utilizing a new photolithography based deep etching method. This method can not only provide lower impedance elements and a reduction in mechanical stress during fabrication, but also provides inherently better imaging due to the superior properties of the piezoelectric single crystal. During Phase I, TRS will establish deep etching for single and multilayer 1.5-D arrays that can allow for frequencies from 5 MHz and above, develop via machining to allow for 2-D elements, and optimize photolithographic methods for multilayering of crystals. In Phase II, TRS expects to develop a 2-D array transducer in conjunction with a medical industry partner. [unreadable] [unreadable] [unreadable]